The invention relates to a device or tool for producing a slot in a human jawbone for receiving, with precise fit, an endossal implant for fastening a denture.
The invention relates furthermore to such an implant, having a post from which two lateral bearing arms extend, which in the direction of the axis of the post have a large extension, and transversely to the axis of the post have a slight extension. The lower edge of each arm constitutes a contact surface at the jawbone.
From prior art German Specification DT-OS 2,505,914 a device is known in which a milling cutter with a cylindrical bearing surface is utilized, having a guide slot which serves as a template for guidance. Since the length of the bearing surface is limited, the guidance is poor.
Since cylindrical millers can function only to a shallow working depth, it is necessary, in the milling of a slot, to utilize a larger number of special cylindrical millers of varying length, and to frequently change the millers. Because the millers can tilt they may break off. Hence the operational time is prolonged. In the case of cylindrical millers, furthermore, the flushing of the cutting surfaces is difficult.
The primary object of the invention is to provide a device which can be simply operated, in which the danger of tool breakage is reduced, the carrying away of the removed bone material and the flushing of cutting surfaces are simplified, and in particular a very precise slot with completely plane lateral surfaces and smooth and precise terminal edges is assured.
The object of the invention is accomplished by means of a circular saw having a circularly curved sawblade, positioned in a housing which partially surrounds the sawblade, and including means for the guidance of the sawblade in a radial direction from the housing.
The sawblade utilized in the device constructed according to the invention, makes possible the production of a slot during the course of an operation without exchanging the cutting tools. Thereby the operational time is on the whole reduced to about one-third of the time previously required. That means a lessening of the danger of infection and an improvement in the prospects for the in-healing of the implant. Precise guidance of the sawblade is assured by its rotational mounting in the housing, so that no lateral grooves are produced in the slot being cut. Additionally the contour of the edge of the slot is precisely defined, so that a correspondingly shaped implant rests exactly with its contact edges against the edges of the slot. In use the sawblade will seldom break, so that even in the case of brief bending loads a loss of the tool cannot occur. In addition to this the sawblade itself, with a corresponding shaping, effects an independent guidance through its lateral surfaces. Since the teeth of the sawblade continuously leave the saw-slot for a certain time, an excellent removal of the sawdust results. The removal of sawdust from the teeth is effected by simple flushing means, which simultaneously removes the flushing medium which flows through the teeth into the slot.
The circularly curved contour of the peripheral edges of the slot is in many cases advantageous, because it adapts itself, particularly in the area of the side teeth, to the shape of the mandibular canal. This is especially advantageous where there is a lower bone height over the mandibular canal and little available space.
In one embodiment of the invention the free part of the sawblade is constantly protected by the upper part of the housing, while the lower part of the housing, through contact surfaces, assures an exact positioning of the saw in relation to the jawbone; particularly, without impairment by the gums, a precise depth of the saw cut is assured.
In another embodiment of the invention sliding rods between the housing parts protect the sawblade, when the housing parts are widely spaced from each other. A fitting pin projecting therefrom fixes the second housing part against lateral movement with respect to the jawbone, so that the forces generated by the saw are transmitted directly to the jawbone, without lateral movements of the housing. Therefore the sawblade can rise freely without binding.
According to an additional feature a stub tube for supplying flushing fluid to the teeth of the sawblade is provided.
Another embodiment renders possible a housing of lesser width in the plane of the sawblade, which in practice is limited to that of the sawblade. For this reason the device can be utilized in small gaps between teeth. A further modification of this embodiment consists of a member having a slot for mounting the sawblade, and bearings on both sides of the slot for rotatably mounting the axle of the sawblade. Positioning bearings on both sides of the axle of the sawblade, improves the guidance and the resistance to wear.
Another structural feature of this embodiment consists in providing on the slide member in the area of the bearings projections extending outwardly from the saw axle, which projections slide in corresponding guide grooves on the inside of the housing. In spite of the small dimensions of the parts, there is assured exact parallel guidance in the direction the saw advances. In addition the sawblade is completely enclosed by the housing in the retracted or partially-advanced position.
In order to be able to utilize fully the advantages of the device constructed according to the invention, the enossal implant previously mentioned is characterized in that the lower edges of the bearing arms lie on a common circular line or circumference. The circularly-shaped lower edges of the implant can be produced quite precisely, and since the peripheral edges of the slot for the implant are also exactly circularly shaped, an extremely uniform positioning of the lower edges of the bearing arms of the implant is assured. This is of advantage for the in-healing process, and for the later load bearing capacity of the implant in use. According to another embodiment, the implant utilizes a base body of metal, which imparts to the implant the desirable characteristics of solidity, rigidity and ease of processing. This base body is provided with a coating, the tissue compatibility of which is greater than that of the metal itself. The material for the coating is selected with reference to high tissue compatibility, so that the implant combines the advantages of a metal implant, with the advantages of a tissue-compatible material.
A suitable coating material is aluminum oxide. This material is so hard that it is not suitable as base material for the implant. As a coating material it covers the total surface of the implant, so as to impart complete tissue compatibility thereto. Titanium oxide is also exceptionally well suited as a coating material. The preferred coating consists of a mixture of 60% Al.sub.2 O.sub.3 and 40% TiO.sub.2. With the aid of the drawings and the following examples the invention should be fully clarified.